How to use TLOAD2 to create half-sine and sine sweep transient loads
Altair Employee
Use case
Two of the main tests required by most vibration test specifications to confirm product qualification, durability, and reliability are the half-sine shock and the sine sweep test.
A shock test is a short duration and non-periodic acceleration impulse defined by a certain shape, duration and amplitude, used to test a system’s capability to survive transient vibrations. These pulses do not necessarily represent real field environments, but they are still used throughout industry to test equipment robustness for convenience.
A simple but useful card to create these types of time-dependent dynamic loads is TLOAD2.
Format and definition
The excitation generated by TLOAD2 follows the following formula:
Which is represented in OptiStruct by the following fields:
Where,
f(t) - Time-dependent dynamic load.
A - Amplitude of the dynamic excitation referenced by the EXCITEID field.
τ -Time delay defined in the DELAY field.
T1 and T2 - Time constants defined in the T1 and T2 fields.
f – Frequency in cycles per unit time defined in F field.
φ – Phase angle in degrees defined in P field.
C - Exponential coefficient defined in C field.
B - Growth coefficient defined in B field.
Examples
Below you can find a few examples of loading curves created by TLOAD2. Attached to this article, there is a simple model with all the loads as well.
20ms half-sine pulse:
A 20ms half-sine is equivalent to a 40ms full sine, thus:
F = 1/0.04s = 25 Hz
The OptiStruct definition will be:
TLOAD2 | SID 11 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
20ms half-sine pulse with delay
TLOAD2 | SID 12 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
or
TLOAD2 | SID 12 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
One cycle sine pulse
TLOAD2 | SID 13 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
Single tone sine at 100Hz
TLOAD2 | SID 14 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
Related Topics
TLOAD2 in OptiStruct Documentation
Response Spectrum Analysis Overview